Contactor with a load current hold-in feature



I l I R. J. FREY CONTACTOR WITH A LOAD CURRENT HOLD-IN FEATURE March 1, 1966 m MK mm M M. m M

United States Patent 3,238,326 CONTACTOR WITH A LGAD CURRENT HQLD-IN FEATURE Robert J. Frey, West Allis, Wis, assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis. Filed June 26, 1964, Ser. No. 378,389 7 Claims. (Cl. 200-87) This invention relates generally to electromagnetic contactors and more specifically to an electromagnetic contactor that utilizes the flux around the movable conductor carrying the load current to hold the movable contact member in engagement with the stationary contact member.

.In the use of electromagnetic contactors there arises a problem of holding the movable contact in engagement with the stationary contact at all times when current is being conducted through the contacts. If the contacts accidentally break due to vibration or other reasons, an arc is drawn which has a deleterious effect on the contacts, often causing them to burn or score to the extent that they are not usable and have to be replaced. In the prior art a separately excited coil and magnetic core are frequently used to initially bring the contacts into engagement and to hold them in engagement. However, if the current to the coil is accidentally lost or falls below a set value while the load current is still being conducted through the contacts, the contacts may separate causing arcing which scores the surface of the contacts.

The contactor of this invention overcomes the problems of the prior art as described above by utilizing a separately excite-d coil and a magnetic frame to initially pull the movable conductor into engagement with the stationary contact so as to carry the load current. The coil and core are designed to provide just sufficient force to overcome the force of the normal resilient means tending to hold the contacts open. A movable yoke of magnetic material is formed around the movable conductor so that when the load current is being carried by the movable conductor a strong magnetic field is formed in this movable yoke. In the engaged position the movable yoke makes contact with the magnetic frame around the coil through a split armature to form a magnetic circuit and supplement the magnetic force tending to hold the movable con-ductor in engagement with the stationary contact. Under high load current conditions, the magnetic force from the load current is sufficient by itself to hold the movable contact in engagement with the stationary contact. Hence, even if the current to the coil of the magnetic frame is cut off, the contacts will not break until the load current has diminished to a sufficient degree that the normal resilient means can overpower the holding force of the magnetic material around the movable conductor. Hence, the contacts cannot be separated until the load. current has been reduced to a safe low level so that when the contacts are separated there is a minimum of arcing and damage to the contacts.

Therefore, it is the object of this invention to provide a new and improved electromagnetic contactor.

Another object of this invention is to provide an electromagnetic contactor that utilizes the load current to create a magnetic field to hold the movable contact in engagement with the stationary contact.

Another object of this invention is to provide a new and improved electromagnetic contactor in which the contacts will not separate until the load current has diminished to a safe level.

Other objects and advantages will be apparent from the following description when read in connection with the attached drawing, in which:

FIG. 1 is a view in side elevation of an electromagnetic contactor embodying this invention;

FIG. 2 is a view taken along the line II-II of FIG. 1; and

FIG. 3 is a view taken along the line IIIIII of FIG. 1.

Referring more specifically to the drawing by characters of reference, the invention is illustrated in an electromagnetic contactor 10. The contactor It) comprises a stationary conductor 11 connected. to a load and a movable conductor 13 connected to a source of electric current. The stationary conductor 11 is provided with a contact 12 and the movable conductor 13 has a contact 14 positioned in alignment with the stationary contact 12. The movable conductor is provided with suitable resilient means such as spring 15 which is positioned to urge the movable conductor out of engagement with the stationary contact. Obviously the connections could. be reversed to connect the movable conductor to the load.

An electromagnet 16 is provided for moving the movable conductor 13 into engagement with the stationary Contact 12. Accordingly, a U-shaped magnetic frame 17 and magnetic core 18 having a suitable coil 19 associated therewith is provided to produce a magnetic force to overcome the resilient means 15 and pull the movable conductor 13 into the operating position. An armature 20 is connected to a magnetic yoke 21 partially surrounding the movable conductor 13 and is pulled against the magnetic frame 17 when the coil 19 is energized. In this position the movable contact 14 firmly engages the stationary contact 12.

In accordance with this invention the armature 20 is split into two parts with each part or half 22, 23 being positioned to engage the ends of both legs 24, 25 of the U-shape-d magnetic frame 17. Each half 22, 23 of the split armature 20 is connected to one leg 26 or 27 of the yoke 21 which surrounds the movable conductor. The purpose of splitting the armature is to create a high reluctance path between the separate halves of the armature and thereby form a pair of parallel paths of lower magnetic reluctance between the yoke 21, one half 22 or 23 of the armature, one leg 24 or 25 of the magnetic frame, the other half of the armature 20 and back to the yoke 21. The reluctance in these paths can be varied by inserting thin, nonmagnetic pieces between the various members in the magnetic circuits or paths such as between the armature and the legs of the frame. The reluctance of the paths would be changed to control the point of drop-out where the contacts would separate.

As the current builds up in the movable conductor in either direction it creates a strong magnetic field in the yoke 21 and the magnetic flux concentrates in the paths of lowest reluctance which include the split armature, the magnetic frame and the movable yoke as described above. The flux in these paths causes the armature and yoke to be held strongly against the legs of the magnetic frame 17 and thereby hold the contact 14 of the movable conductor 13 in firm engagement with the contact 12 of the stationary conductor 11. Hence, if the current to the coil 19 of the magnetic frame is cut off for any reason there is sufficient force from the magnetic field o fthe yoke 21 to hold the armature against the magnetic frame and the contacts 12, 14 in engagement. In fact, it may be desirable to cut off the current to coil 19 when the load current reaches the operating value.

The contacts 12, 14 will remain engaged until the current in the movable conductor drops below a predetermined safe value. Then if the current to coil 19 is cut off, the force of the resilient member takes over and causes the movable conductor to break away from the stationary conductor. At this low current value there is a minimum of arc and, hence, a resulting minimum of scoring and wear on the contacts 12, 14.

In operation, current is directed to the starting coil 19 which causes the armature 20 to move against the magnetic frame 17 pulling the contact 14 on the movable conductor 13 into engagement with the stationary contact 12. As current flows in the movable conductor it creates a magnetic field that concentrates in the movable yoke 21 that is in a pair of parallel low reluctance magnetic paths that include the armature and the magnetic frame. As long as the load current being carried by the movable conductor remains above a predetermined level, the contacts will not open. However, when the load current does fall below this level, the current to coil can be cut off and the resilient means 15 will then force the movable conductor away from the stationary contact to break the load circuit.

Although but one embodiment of the present invention has been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

Having now particularly described and ascertained the nature of my said invention and the manner in which it is to be performed, I declare that what I claim is:

1. A contactor comprising a stationary and movable contact means, a magnetic frame, a coil associated with said frame for producing a magnetic flux therein, a movable conductor connected to said movable contact means, a yoke partially surrounding said movable conductor, an armature interposed between said movable conductor and said magnetic frame, said armature being connected to and movable with said yoke and said movable conductor, said armature being split so as to form a low reluctance magnetic path around said movable conductor that includes said yoke, said armature and said magnetic frame to increase the holding force on said movable conductor as current passes through said contact means and said movable conductor.

2 A contactor comprising a stationary and movable contact means, a U-shaped magnetic frame, a coil associated with said frame for producing a magnetic flux therein, a movable conductor connected to said movable contact means, a yoke partially surrounding said movable conductor, an armature interposed between said movable conductor and said magnetic frame, said armature being connected to and movable with said yoke and said movable conductor, said armature being split into two parts so as to form a pair of low reluctance mag netic paths around said movable conductor that include said yoke, said armature and said magnetic frame to increase the holding force on said movable conductor as current passes through said contact means and said movable conductor.

3. A contactor comprising a stationary and movable contact means, a magnetic frame, said frame comprising a pair of legs and a connecting bar to form a U- shaped member, a coil associated with said frame for producing a magnetic flux therein, a movable conductor connected to said movable contact means, a yoke partially surrounding said movable conductor, an armature interposed between said movable conductor and said magnetic frame, said armature being connected to and movable with said yoke and said movable conductor, said armature being split into two parts, each part of said armature positioned to engage both legs of said frame to form a pair of parallel low reluctance magnetic paths around said movable conductor, each of said paths including said yoke, said armature and one of said legs of said magnetic frame to increase the holding force on said movable conductor as current passes through said contact means and said movable conductor.

4. The contactor of claim 3 in which means are provided for varying the reluctance of said magnetic paths.

5. A contactor comprising a stationary and movable contact means, a movable conductor connected to said movable contact means, a yoke partially surrounding said movable conductor, a magnetic frame, an armature interposed between said movable conductor and said magnetic frame, said armature being connected to and movable with said yoke and said movable conductor, a coil associated with said frame for producing a magnetic flux therein, means for energizing said coil to move said armature into engagement with said frame and said movable contact into engagement with said stationary contact to complete a circuit and cause said movable conductor to carry a current, said armature being split so as to form a pair of low relutance magnetic paths around said movable conductor that includes said yoke, said armature and said magnetic frame to increase the holding force on said movable conductor as current passes through said contact means and said movable conductor.

6. A contactor comprising stationary contact means connected to a source of high current, movable contact means, a movable conductor connected to said movable contact means, a yoke partially surrounding said movable conductor, a magnetic frame, an armature interposed between said movable conductor and said magnetic frame, said armature being connected to and movable with said yoke and said movable conductor, a coil associated with said frame for producing a magnetic flux therein, means for energizing said coil to move said armature into engagement with said frame and said movable contact into engagement with said stationary contact to connect said movable conductor with the source of high current, said armature being split into two parts to form a high reluctance path therebetween and a pair of low reluctance magnetic paths around said movable conductor that include said yoke, said armature and said magnetic frame to increase the holding force on said movable conductor as current passes through said contact means and said movable conductor, and means for deenergizing said coil when current is passing through said movable conductor.

7. A contactor comprising stationary contact means connected to .a source of high current, movable contact means, a movable conductor connected to said movable contact means, a yoke partially surrounding said movable conductor, a magnetic frame, said frame comprising a pair of legs and a connecting bar arranged to form a U-shaped member, an armature interposed between said movable conductor and said magnetic frame, said armature being connected to and movable with said yoke and said movable conductor, a coil associated with said frame for producing a magnetic flux therein, means for energizing said coil to move said armature into engagement with said frame and said movable contact into engagement with said stationary contact to connect said movable conductor with the source of high current, said armature being split into two parts to form a high reluctance path therebetween, each of said armature parts being positioned to span both of said legs to form a pair of parallel low reluctance magnetic paths around said movable conductor that include said yoke, said armature and one of said legs of said magnetic frame to increase the holding force on said movable conductor as current passes through said contact means and said movable conductor.

References Cited by the Examiner UNITED STATES PATENTS 2,679,561 5/1954 Thompson 200-87 BERNARD A, GILHEANY, Primary Examiner, 

1. A CONTACTOR COMPRISING A STATIONARY AND MOVABLE CONTACT MEANS, A MAGNETIC FRAME, A COIL ASSOCIATED WITH SAID FRAME FOR PRODUCING A MAGNETIC FLUX THEREIN, A MOVABLE CONDUCTOR CONNECTED TO SAID MOVABLE CONTACT MEANS, A YOKE PARTIALLY SURROUNDING SAID MOVABLE CONDUCTOR, AN ARMATURE INTERPOSED BETWEEN SAID MOVABLE CONDUCTOR AND SAID MAGNETIC FRAME, SAID ARMATURE BEING CONNECTED TO AND MOVABLE WITH SAID YOKE AND SAID MOVABLE CONDUCTOR, SAID ARMATURE BEING SPLIT SO AS TO FORM A LOW RELUCTANCE MAGNETIC PATH AROUND SAID MOVABLE CONDUCTOR THAT INCLUDES SAID YOKE, SAID ARMATURE AND SAID MAGNETIC FRAME TO INCREASE THE HOLDING FORCE ON SAID MOVABLE CONDUCTOR AS CURRENT PASSES THROUGH SAID CONTACT MEANS AND SAID MOVABLE CONDUCTOR. 